This chapter introduces SC circuits. A brief description is given for the main building blocks of a SC filter (operational amplifiers, switches, capacitors, and non-overlapping clock phases). A few examples of SC resistor emulation circuits are presented along with their equivalent resistance. Two examples of SC integrators are also shown, one with the resistors implemented with a T branch (parasitic-sensitive integrator) and another with a branch in π (parasitic-insensitive integrator). A signal flow graph is presented which allows large circuits to be analyzed graphically. The chapter ends with the two Sallen-Key topologies designed in this book, in their continuous time version.